Various techniques for electrostatic image transfer are known. One method includes the use of an intermediate transfer member. A liquid image, which includes a liquid carrier having ink particles dispersed therein, is transferred from a photoconductive surface of a photoconductive member or drum to a surface (e.g., a release layer or blanket) of the intermediate transfer member. The liquid image is attracted from the photoconductive surface to the surface of the intermediate transfer member. The liquid carrier is removed from the surface of the intermediate transfer member and the ink particles are compacted on the surface in the image configuration. Thereafter, the ink particles are transferred from the surface of the intermediate transfer member to a substrate in the image configuration by electrostatic attraction.
Modern liquid toner electrostatic imaging began with the invention of a new class of toners referred to as ElectroInk™. This type of toner is characterized by its toner particles being dispersed in a carrier liquid, where the toner particles include a core of a polymer with fibrous extensions extending from the core. When the toner particles are dispersed in the carrier liquid in a low concentration, the particles remain separate. When the toner develops an electrostatic image, the concentration of toner particles increases and the fibrous extensions interlock. A large number of patents and patent applications are directed toward this type of toner (e.g., U.S. Pat. Nos. 4,794,651; 4,842,974; 5,047,306; 5,407,307; 5,192,638; 5,208,130; 5,225,306; 5,264,312; 5,266,435; 5,286,593; 5,300,390; 5,346,796; 5,407,771; 5,554,476; 5,655,194; 5,792,584 and 5,5923,929 and PCT Patent publication WO/92/17823, the entire disclosures of all of which are incorporated herein by reference).
It has been discovered that this type of toner allows for high quality offset printing at high speed. This type of printing is described the following U.S. Pat. Nos. 4,678,317; 4,860,924; 4,980,259; 4,985,732; 5,028,964; 5,034,778; 5,047,808; 5,078,504; 5,117,263; 5,148,222; 5,157,238; 5,166,734; 5,208,130; 5,231,454; 5,255,058; 5,266,435; 5,268,687; 5,270,776; 5,276,492; 5,278,615; 5,280,326; 5,286,948; 5,289,238; 5,315,321; 5,335,054; 5,337,131; 5,376,491; 5,380,611; 5,426,491; 5,436,706; 5,497,222; 5,508,790; 5,527,652; 5,552,875; 5,555,185; 5,557,376; 5,558,970; and 5,570,193; the entire disclosures of which are incorporated herein by reference.
Color shifting pigments and colorants (e.g., special-effect pigments) have been used in numerous applications, ranging from automobile paints to anti-counterfeiting inks for security documents and currency. Such pigments and colorants exhibit the property of changing color upon variation of the angle of incident light, or as the viewing angle of observer is shifted. The primary method used to achieve such color shifting colorants is by dispersing small flakes, which are typically comprised of multiple layers of thin films having particular optical characteristics, throughout a medium such as paint or ink that may then be subsequently applied to the surface of an object.
The color shifting properties of the colorant can be controlled through proper design of the optical coatings or films used to form the flakes. Desired effects can be achieved through the variation of parameters such as thickness of the layers forming the flakes and the index of refraction of each layer. The changes in perceived color which occur for different viewing angles or angles of incident light are a result of a combination of selective absorption of the materials including the layers and wavelength dependent interference effects. The absorption characteristics of a material as well as interference phenomena are responsible for the basic color that is observed. The interference effects, which arise from the superposition of the light waves that have undergone multiple reflections and transmissions within the multilayered thin film structure, are responsible for the shifts in perceived color with different angles. Thus, use of the special-effect pigments requires that the layers of the special-effect pigments be intact in the ink formulation.